The south-western Indian Ocean islands, excluding the microcontinent of Madagascar, are geologically complex and diverse. They have been subject to drastic sea level changes, volcanic events and anthropogenic changes, all of which have contributed to confuse understanding of their avian biogeography. An array of factors have affected these avifaunas, based on palaeontological, historical and molecular evidence,which together have shown that avian biogeography is not congruent with the relative age and size of the islands.